The present disclosure relates to a liquid crystal display device including a liquid crystal display element, in which a liquid crystal layer is sealed between a pair of substrates.
As of recent, liquid crystal display (also simply “LCD”) devices have come to be widely used as display monitors in liquid crystal television receivers, laptop computers, automotive navigation devices, and so forth. Such liquid crystal display devices are classified into several display modes (formats) depending on the molecular array (alignment) of liquid crystal molecules included in a liquid crystal layer held between substrates. An example of a common display mode is the twisted nematic (TN) mode, in which the liquid crystal molecules are arrayed in a twisted state with no voltage applied. In the TN mode, the liquid crystal molecules exhibit positive dielectric constant anisotropy. That is to say, the liquid crystal molecules have a nature that the dielectric constant in the longitudinal axis direction is greater than that in the lateral axis direction. Accordingly, a TN mode liquid crystal display device has a structure where the liquid crystal molecules are ordered in a direction perpendicular to a substrate face, having sequentially rotated the alignment orientation thereof within a plane parallel to the substrate face.
On the other hand, there is increased interest in a vertical alignment (VA) mode, where the liquid crystal molecules are aligned perpendicular to the substrate face with no voltage applied. In the VA mode, the liquid crystal molecules exhibit negative dielectric constant anisotropy. That is to say, the liquid crystal molecules have a nature that the dielectric constant in the longitudinal axis direction is smaller than that in the lateral axis direction. This allows a boarder view angle to be realized as compared to the TN mode.
This VA mode liquid crystal display device is configured such that applying voltage causes the liquid crystal molecules aligned perpendicular to the substrate to respond by tilting in the parallel direction as to the substrate due to the negative dielectric constant anisotropy, thus transmitting light. However, the direction in which the liquid crystal molecules aligned perpendicular to the substrate tilt is unprescribed, so applying voltage disturbs the alignment of the liquid crystal molecules. This has been a factor in poor responsivity to voltage.
Accordingly, various proposals have been made as techniques to restrict the alignment of the liquid crystal molecules when voltage is applied. Examples include a multi-domain vertical alignment (MVA) format, a patterned vertical alignment (PVA) format, and a technique using a photo-alignment film (see Japanese Unexamined Patent Application Publication No. 5-232473, for example). The MVA format realizes a wide view angle while controlling alignment using slits and ribs (protruding portions). As of recent, there has also been proposed what is called a fine-slit structure, where multiple fine slits are formed in electrodes formed at one substrate (specifically, pixel electrodes) and a slit-less solid electrode (specifically, the common electrode) formed on the other substrate. See Japanese Unexamined Patent Application Publication No. 2002-357830, for example. However, the fine-slit structure has a problem in that there are portions of slits formed of fine line-and-space patterns where the electrical field is not applied, and further, the liquid crystal molecules are in a twisted aligned state near the edges of the lines when voltage is applied, which has resulted in lower light transmittance.
Japanese Unexamined Patent Application Publication No. 2011-232736 discloses a technology in which a portion with ridges and grooves are formed is provided to the pixel electrodes instead of the multiple fine slits, as a technology aiming to solve this problem. The multiple ridge-and-groove portions in one pixel are formed of trunk ridges extending on the X axis and the Y axis, and multiple branch ridges extending from the longitudinal sides of the trunk ridges toward the perimeter of the pixel. The longitudinal side portions of the trunk ridges where branch grooves are not joined are parallel with the X axis or Y axis. An alignment film, fashioned after the ridges and grooves, is formed threabove.